Aspirator jet for drawing-off filaments

ABSTRACT

In an aspirator jet for drawing-off thermoplastic filaments having a nozzle and a throat, the primary aspirating air is smoothly expanded to supersonic velocities through a throat into an outwardly diverging expansion chamber which is preferably dome-shaped. A guide tube for the filaments and secondary air extends centrally through the throat and through the expansion chamber to the draw-off tube, which has a constant diameter. The design is such that the aspirating air flows parallel to the filaments issuing from the guide tube and goes not impinge thereon as is the case with the jet designs of the prior art. This design permits draw-off of filaments at high speeds, in excess of 2,000 meters/min., with good separation and substantially complete parallelism between the filaments and without intermingling or twisting and interlocking of the filaments.

April 1972 o. DORSCHNER T 3,655,862

ASPIRATOR JET FOR DRAWINGOFF FILAMENTS 2 Sheets-Sheet 1 Filed Aug. 15,1969 April 11, 1972 o, DORSCHNER ETAL 3,655,862

ASPIRATOR JET FOR DRAWING-OFF FILAMENTS Filed Aug. 15, 1969 2Sheets-Sheet 2 United States Patent ASPIRATOR JET FOR DRAWING-OFFFILAMENTS Oskar Dorschuer, Bad Hamburg, Franz Josef Carduck,

Bergen-Enkheim, Nordring, Christoph Storkebaum,

Egelsbach, and Claus Rother, Petterweil, Germany, as-

signors to Metallgesellschaft AG, Frankfurt am Main,

Germany Filed Aug. 15, 1969, Ser. No. 850,500 Claims priority,application Germany, Aug. 17, 1968, P 17 85 158.0 Int. Cl. B29c 17/02U.S. Cl. 264-290 11 Claims ABSTRACT OF THE DISCLOSURE In an aspiratorjet for drawing-01f thermoplastic filaments having a nozzle and athroat, the primary aspirating air is smoothly expanded to supersonicvelocities through a throat into an outwardly diverging expansionchamber which is preferably dome-shaped. A guide tube for the filamentsand secondary air extends centrally through the throat and through theexpansion chamber to the draw-oil? tube, which has a constant diameter.

The design is such that the aspirating air flows parallel to thefilaments issuing from the guide tube and does not impinge thereon as isthe case with the jet designs of the prior art.

This design permits draw-01f of filaments at high speeds, in excess of2,000 meters/min., with good separation and substantially completeparallelism between the filaments and without intermingling or twistingand interlocking of the filaments.

PRIOR ART In the production of non-woven webs, mats, layers and similarproducts from continuous filaments, the molten raw materials areextruded through spinning orifices and the spun yarn is generallydrawn-0E by pneumatic jets and blown onto the lay-down surface. Suchprocesses for the production of non-woven materials and the pneumaticjets used are described, for example, in British Pat. No. 932,482 and inUS. Pat. No. 3,341,394. The use of pneumatic jets, usually referred toas aspirator jets or air jets, allows high draw-01f speeds. As a greatnumber of filaments can be routed through one jet, the production speedsfor the non-woven product are high which is very much desired from theaspect of low production costs. Compressed air is generally supplied tothe jets to serve as the moving medium. To achieve high draw-off speedsin jets, the moving air is generally accelrated by expansion tosupersonic velocity and directed at a small angle against the filamentsrunning through the jet. This exerts a tension on the filaments which,with filaments of thermoplastic organic plastics, efiects drawing andorientation of the filaments. To achieve special effects, e.g. crimpingof the filaments, hot air or steam instead of air can be used.

Several different designs of draw-ofi' jets are known. They all have incommon a funned-shaped inlet port for the filament bundles whichfinishes up in a cylindrical or almost cylindrical filament guidechannel. 'In this filament guide channel or at the end of it, theexpanding or expanded aspirating gas is directed toroidally at an angleof about 5l5 against the filaments. When the aspirating gas isintroduced around the end of the cylindrical filament inlet, theexternal wall at the lower end of the filament inlet pipe has beengenerally tapered downwardly to facilitate the tangential impingement ofaspirating gas. Because of the friction efiect which the aspirating gasexerts on the filament bundle, the filament is 'ice drawn through thejet at a speed which is greater than the spinning speed.

With some jet designs the filaments may flutter, swing to and fro andintermingle (see British Pat. No. 1,088,931).

A properly produced non-woven web made in this manner contains parallelextending filaments which mutually cross each other at random intervalsand which may overlap backwardly. To prevent converging or bandingtogether of the filaments at high filament draw-off speeds, thefilaments usually are electrostatically charged, e.g. by means of coronadischarge devices or by the application of a tribe-electric charge. (SeeUS. Pat. No. 3,341,394 and British Pat. No. 932,482.) The electrostaticrepulsion between the like-changed filaments prevents a converging ofthe filaments. A disadvantage with these methods is that special devicesfor charging the filaments are required. In addition, it is necessary tobring the draw-off jets to the same potential as the filaments toprevent the filaments from sticking to the jet wall. The application ofsuch processes using electrostatic charging of the filaments demandsspecific electric properties of the filament material which a number ofmajor raw material, such as polypropylene and polyethyleneterephthalate, do not possess. Such raw materials have to be treated insome manner to improve their electric properties to render them suitablefor electrostatic charging. The introduction of sulfonated comonomers orinorganic salts for this purpose into the organic polymer structure, ashas been done, complicates and further increases costs. Apart fromelectrostatic charging of the filaments, little is known as to how theundesired mutual interference of the filaments at high draw-oft speedscan be eliminated. Subsequent improvements of the original methods stilluse electrostatic charging of the filaments (see US. Pat. Nos.3,293,718, 3,364,538, 3,314,122, and 3,368,934).

The same problem exists with flat or slotted jets. With flat 0r slottedjets the moving medium is directed at an angle through the twolongitudinal sides of the rectangular filament opening (see US. Pat. No.3,302,237). When intermingling of the filaments at high draw-off speedsis not desired, electrostatic charging cannot be dispensed with (see US.Pat. No. 3,364,538). Attempts have been made to eliminate interminglingof filaments by using adequate jet designs (see US. Pat. No. 3,286,896).To achieve this aim, the turbulence in the jet was reduced. On the otherhand, a certain turbulence is needed in order to achieve the necessarytension on the filaments. To meet these requirements, a jet design wasused in this patent wherein air was admitted at two points located beloweach other. However, this method did not render electrostatic chargingof the filaments unnecessary.

It is further desirable that the jets draw-in through the filament inletport a certain amount of secondary air so that in the event of filamentbreakage the filament can easily be reintroduced into the filament inletport. High draw-off speeds with complete parallel arrangement of thefilaments and without electrostatic charging and adequate aspiration ofsecondary air through the filament inlet port have so far beenincompatible requirements.

THIS INVENTION The object of the present invention is to provide a jetfor the draw-off of filaments which positively prevents mutualinterference of the filaments, without the need for additionalelectrostatic charging of the filaments or the jet, even at highdraw-off speeds above 2000 m./min. and where the aspirated secondary airat the end of the filament guide channel reaches at least soundvelocity. The jet of this invention is in particular suitable for use inthe production of non-woven products from deposited continuous filamentswhere the spinnable material is extruded through spinnerets, drawn-offand laid down on a moving receiving surface, such as web, mat or thelike.

The invention relates to a jet for withdrawing a single filament or aplurality of filaments in which a tension is applied to the filaments bythe aspirating medium expanding to supersonic velocity, with a narrowinginlet port for the filaments which finishes up in a guide channelextending through the smallest cross-section of the jet. This jet ischaracterized by the expansion chamber enlarging outwardly below thenarrowest jet cross-section. The enlargement of the expansion chambercan be conical but a curved dome-shaped enlargement of the expansionchamber is preferred.

The aspirating gas is accelerated to sound velocity when it reaches thenarrowest jet cross-section and in the expansion zone below it isexpanded to Mach figures of up to 3.5 and higher either parallel to thedirection of the filaments or away from the direction of the filamentsdepending upon the motive pressure and the ratio between exitcross-sectional area and inlet cross-sectional area of the expansionzone.

Compared to the conventional jet designs, the present inventiondeliberately avoids having the aspirating gas impinge the filaments atan angle. This is achieved by outwardly enlarging the expansion chamberbelow the narrowest jet cross-section or throat of the jet and byarranging the outer boundary of the guide channel such that it extendsthrough the narrowest jet cross-section, cylindrically or by expandingit in the downstream direction.

The aspirating gas expansion chamber is bounded at its inlet by thethroat, i.e., the narrowest cross-section of the jet. The outlet of theexpansion chamber ends at or prior to the orifice plane of the end ofthe filament guide channel. The outward enlargement of the expansionchamber can be realized in different ways. A tapered enlargement can beused with round jets and a rectilinear or an almost rectilinearenlargement can be adopted for slotted jets. To provide for parallelflow and smooth expanson of the aspirating gas, a dome-shapedenlargement is preferable. The transition from the throat of the jetopening to the draw-oft conduit consists of a wall which has preferablya curvilinear section. A tangent of the section, measured against thevertical, has an angle of 8 to 20, preferably 10 to To ensure that thesecondary air drawn in through the guide channel has at least soundvelocity at the end of the guide channel and to eliminate interminglingof the filaments passing through the jet, the ratio between exitcross-section and inlet cross-section of the expansion zone desirablydoes not exceed 10:1. A ratio of between 7:1 and 3:1 is preferred.

Air is preferably used as the aspirating gas in the jet of thisinvention. The air can be cold or warm. However, steam or any othersuitable medium can also be used. The gas is supplied to the jet atpressures higher than those used with conventional pneumatic filamentdraw-01f jets. The inlet pressure of the gas is preferably between 10and 50 atmospheres gauge. It is so chosen that at a predetermined ratiobetween exit cross-section and inlet cross-section of the expansion zonethe secondary air drawn in through the inlet port reaches at least soundvelocity by the time it reaches the end of the guide channel. The lowerend of the guide channel is preferably bevelled from the inside to theoutside, or outwardly tapered.

At a ratio between exit cross-section and inlet crosssection of theexpansion zone of, say, 4.9: 1 and a pressure of the primary air of 22atmospheres gauge, a static head of 0.5 atmospheres absolute is achievedin the orifice plane of the end of the guide channel so that thesecondary air drawn in through the inlet port just reaches soundvelocity. The Mach number of the expanded primary air stream is 3.15.

With an area ratio of 6:1 and with the same pressure of the primary airof 22 atmospheres gauge, the static head in the orifice plane of theguide channel is reduced to 0.37 atmospheres absolute. The velocity ofthe expanded moving stream reaches a Mach number of 3.36. The aspiratedsecondary air reaches a Mach number of 1.3.

The outer boundary or surface of the guide channel can have a constantdiameter end to end, although it is preferred in some cases to have theguide channel expand at its lower end as this contributes to theseparation of the filaments.

The guide tube can be arranged to be adjustable with respect to theexpansion chamber whereby the ratio between exit cross-section and inletcross-section of the expansion zone can be varied. The inletcross-section or throat is the area between outer boundary of the guidechannel and narrowest part of the jet. The exit cross-section is thearea between the lower end of the guide channel and the boundary of theexpansion chamber or draw-off channel. With round jets, both areas arecircular. With constant motive pressure, it is generally not necessaryto vary the set area ratio during operation. The jets are preferably sodesigned that during normal operating conditions the lower end of thefilament guide channel terminates about 1 to 2 mm. below the transitionpoint of the enlargement of expansion chamber and the beginning of thedraw-off channel.

To prevent intermingling of the filaments, the filament draw-off channelshould have a uniform cross-section from end to end and its lengthshould not exceed 150 times its diameter. The length of the filamentdraw-off channel is generally at least 20 times, preferably 30 to timesits diameter. In the case of slotted jets, the width of the rectangularfilament draw-off channel is substituted for the diameter.

The length of the guide channel, which extends through the narrowest jetcross-section and in whose orifice plane the expansion zone finishes,should be 10 to 40 times, preferably 15 to 30 times its diameter (withround jets) and its width (with slotted jets) respectively.

The conical inlet port of the jet for the filaments and for thesecondary air should be so arranged that the angle between inlet portwall and the vertical is between 5 and 15. The angle is normally sochosen that it lies between 7 and 11.

In the case of round jets, the aspirating gas is first passed throughone horizontal or two oppositely arranged horizontal boreholes into anannular hold-back or plenum chamber. The inner boundary of the hold-backchamber is formed by a baffle, the upper end of which is located so highthat the admitted moving medium cannot pass direct into thefunnel-shaped jet opening. The hold-back chamber checks the incomingstream and reverses it upwardly at low velocity before it enters thefunnel-shaped jet opening and reaches sound velocity in the narrowestcross-section of the jet.

The generating angle of the funnel-shaped jet opening, i.e. the anglebetween jet opening wall and the vertical can vary between 20 and 50. Itnormally ranges between 25 and 40. The hold-back chamber and the shapeand size of the jet opening have to be suitably adapted to each other sothat the velocity of the incoming medium stream is between A and A;Mach, preferably between /5 and Mach at the beginning of the jetopening. After passing through the narrowest jet cross-section themedium stream is expanded to supersonic velocity in the outwardlyenlarging expansion chamber. After expansion, a negative pressure ofabout 0.1 to 0.5 atmospheres absolute is established in the orificeplane of the guide channel. In the design of the jet of this invention,expansion takes place at a minimum of pressure drop. The secondary airdrawn in through the guide channel reaches at least sound velocity atthe guide channel outlet. The strong aspiration of atmospheric airfacilitates considerably the threading of filaments through the inletopening of the jet.

The drawings:

FIG. 1 is an elevational view in section of a. round jet of thisinvention;

FIG. 2 is an elevational view in section of a portion of a jet of thisinvention;

FIG. 3 is an elevational view in section of a portion of an alternativedesign; and

FIG. 4 is an elevational view of a slotted jet embodying the teachingsof this invention.

In FIGS. 1-3, the same members are used to identify like parts.

DESCRIPTION The round jet of this invention illustrated in FIG. 1consists of lower part 1 and upper part 2 bolted to the lower part.Upper part 2 accommodates conical inlet funnel 3 for filaments andsecondary air, the inner wall of which finishes up downwardly in guidetube 4. At point 5, upper part 2 and lower part 1 are provided with finethread, and at point 6 both parts are ground. The ground portions andthe threads are so arranged that the two parts fit properly. Conicalinlet opening 3 has a generating angle a (see FIG. 1) of to 15,preferably 7 to 11". This, in conjunction with the maintenance of theother critical dimensions of the jet of this invention, aids in theseparating of the filaments before, in and after the jet.

Inlet funnel 3 finishes up downwardly in guide tube 4 and upwardly witha relatively small radius of curvature at opening 8. The height of inletfunnel 3, i.e. the distance between the transition of the inlet funnelto opening 8 and the transition of the inlet funnel to guide tube 4 mustnot exceed 40 times the inside diameter of guide tube 4. A height of theinlet funnel of to 20 times the inside diameter of tube 4 is preferred.The external wall of guide tube 4 finishes upwardly in a rounded corner9 and lower horizontal boundary surface 10 of upper part 2.

Lower part 1 has a central borehole, the inner wall of which is groundin its upper portion and provided with fine thread in its lower portionso that the upper part 2 can be screwed to the lower part. Horizontalborehole 11 extends through lower part 1 for the supply of the primaryaspirating air and ends in annular holdback chamber 12. To eliminatetorsional force on the air, which would cause curling of the individualfilaments, it is preferable to provide two boreholes 11 displacedrelatively to each other at an angle of 180 for the supply of the air tohold-back chamber 12 vertically to the direction of the filaments. Thehold-back chamber is bounded inwardly by vertical bafiie walls 13, whichend upwardly in a circular corner 14 connecting with funnel-shaped jetopening 15. Jet opening 15 tapers in the form of a funnel up to thenarrowest point or throat 16. Below the narrowest point 16 the jetenlarges outwardly and ends in cylindrical draw-01f tube 18. In the jetpresented in FIG. 1, the expansion chamber conically enlarges outwardly.The conical boundary wall of expansion chamber 17 commences tangentiallyfrom the circular edge at the narrowest point 16. The angle 5 betweenthe tangent and the vertical is 8 to 20", preferably 10 to 15.

The outer wall of guide tube 4 forms with the narrowest point 16 anannular throat up to which the aspirating gas is accelerated to soundvelocity and passes downwards into expansion chamber 17. Rounded-01fportion 9 and lower surface 10 of the upper part form the upper boundaryof hold-back chamber 12. Rounded-off portion 9 favors turbulent-freereversing of the moving medium into the jet funnel 15. The generatingangle (see FIG. 1) of jet funnel 15 should be between 20 and 50.

The length of guide tube 4 below the narrowest point 1.6 can be variedby screwing upper part 1 more or less deep into lower part 2. Undulydeep screwing of upper part 1 into lower part 2 is prevented by annnularsupporting surface 7 which contacts an appropriate boundary surface ofthe upper part.

The annular opening between the outer wall of guide tube 4 and narrowestpoint 16 is the smallest jet crosssection and at the same time is theinlet cross-section of expansion chamber 17. In the jet illustrated inFIG.1, guide tube 4 has uniform cylindrical outside diameter from top tobottom. The lower end of the inner part of guide tube 4 is enlargedoutwardly like a funnel, ending in the orifice plane of the guide tube19.

The annular area between the end of guide tube 4 and the beginning ofdraw-off tube 18 (i.e., the end of expansion chamber 17) forms the exitcross-section of the expansion zone. The end of the guide tube islocated somewhat below the beginning of draw-off tube 18. Draw-oif tube18 is uniformly cylindrical from top to bottom.

FIG. 2 shows an elevational view of the expansion chamber of anotherdesign. The outside of guide tube 4 is uniformly cylindrical from top tobottom. The inner part of guide tube 4 tapers towards lower end 19outwardly like a funnel. Below the narrowest jet cross-section 16,expansion chamber 17 enlarges curvilinearly (in cross-section). Thecircular connecting edge 16 between jet funnel 15 and expansion chamber17 extends downwardly. A tangent thereto forms, with the vertical, theangle )9.

FIG. 3 shows an elevational view of the expansion chamber of another jetof this invention. As before, the lower inner end of guide tube 4 isenlarged outwardly. The outer lower end 20 of guide tube 4 also isoutwardly enlarged and in the elevation it forms with the vertical theangle 8.

FIG. 4 shows an elevational view of a rectangular or slotted jet of thisinvention. Inset 32 accommodates inlet port 33 for the filaments andsecondary air, which continues downwards into guide channel 34 whoselower inner (49) and lower outer (50) boundary is enlarged outwardly.Attached to the two longitudinal members 31 with boreholes 41 for theaspirating gas are connecting members 35 and 36. Members 35 and 36 areso shaped that after connection of the two longitudinal members bytransverse members 31, members 35 and 36 form in conjunction with inset32 the jet. The bafiles in the plenum chambers 42 are marked 42 with 43and end in transition edges 44. The circular edges at the narrowest jetportion or throat are marked 46 and the longitudinal boundaries of thedraw-off channel 48. Several inlet ports 41, which are equallydistributed over the length of the jet, end in the two hold-backchambers 42. The inlets to the throat are marked 45, the expansionchambers 47 and the circular transition of bafiles 43 to the inlet ports44.

The critical dimensions have to be chosen the same as for the circularjets of this invention except that the width of the rectangularcross-section is to be substituted for the diameter.

EXAMPLE 1 A jet of this invention according to FIG. 1 has the followingcharacteristic dimensions:

Cross-sectional area of the expansion zone (17) inlet (or throat)2 mm.

Cross-sectional area of expansion zone exit10 mm.

Ratio between exit cross-sectional area and inlet crosssectional area ofexpansion zone-5:1

Diameter of draw-off tube 184.35 mm.

Length of draw-off tube 18250 mm.

Length of guide tube 430 mm.

Outside diameter of guide tube 42.5 mm.

Inside diameter of guide tube 4-2. mm.

Generating angle a of inlet funnel 3-8 Generating angle '7 of jet funnel1530 Radium in the narrowest cross-section at point 16-2 mm.

The jet was operated on cold air. The motive pressure was 22 atmospheresgauge and air consumption was 30 standard cubic meters per hour. The jetwas arranged below a melt extruder from which the filaments were spun.The filament draw-01f speed was 3,400 m./min. The filaments had a denierof 3 den. and were blown onto a constantly moving lay-down receiver toform a web of irregularly crossing bundles of parallel filaments.Converging of filaments, twisting, interlacing and intermingling of thefilaments did not occur. Special electrostatic charging of the filamentswas not applied.

EXAMPLE 2 In the same round nozzle described in Example 1, 150' freshlyspun filaments from polypropylene were drawnolf with equally goodsuccess and deposited to form a web. The filaments had a denier of 4.8den. The drawoff speed was 2,100 m./min. The other operating conditionswere the same as in Example 1.

EXAMPLE 3 A jet according to FIG. 3 had the following dimensions:

Diameter of narrowest cross-section (at 16) 3 mm.

Angle B9 Angle 6-3 Inside diameter of guide tube 4, prior to taper2.0mm.

Outside diameter of guide 4, prior to taper2.5 mm.

Ratio between exit cross-sectional area and inlet crosssectional area ofexpansion zone-5.7:1

Air at 28 atmospheres gauge was used as motive air. Air consumption wasM standard-cubic meters per hour. 26 filaments of nylon-6 with a denierof 9 den. were drawn-off at a speed of 3,000 m./ min.

The jets of this invention can be used for drawingoif all materialswhich form filaments. Such materials include mainly polyolefins,polyamides, and polyesters.

What is claimed is:

1. An aspirator jet for drawing-off thermoplastic filaments comprising:

(a) a nozzle having a throat with a funnel-shaped inlet and a smoothlyexpanding outlet;

(b) an inlet conduit for admitting primary aspirating gas under pressureto said funnel-shaped inlet;

(c) a centrally located guide conduit extending through saidfunnel-shaped inlet, said throat, and said expanding outlet andterminating at or after the end of said expanding outlet,

(i) said guide conduit having at its upper end an outwardly taperedinlet port opening to the at mosphere,

(ii) the lower portion of said guide conduit extending through saidthroat and said expanding outlet having a uniform outside diameter andforming with said expanding outlet an expansion chamber for primaryaspirating gas passing through said throat which chamber enlargesdownwardly in cross-section from said throat; and

(d) a draw-ofi? conduit having a uniform cross-section from end to endcoupled with said expanding outlet and continuing downstream therefrom.

2. Aspirator jet of claim 1 wherein the ratio of the opencross-sectional area of the end of said expansion chamber to the opencross-sectional area of said throat is in the range of 7:1 to 3:1.

3. Aspirator jet of claim 1 wherein said expansion chamber has a curveddome-shape.

4. Aspirator jet of claim 1 wherein said guide conduit has a length inthe range of 10 to 40 times its smallest inside width and said draw-offconduit has a length in the range of 20 to times its width.

5. Aspirator jet of claim 4 wherein said expansion chamber has a domeshape and wherein the terminal end of said guide conduit downstream ofsaid throat internally expands outwardly.

6. The aspirator jet of claim 1 wherein the external terminal end ofsaid guide conduit expands outwardly downstream of said thorat.

7. Aspirator jet of claim 1 wherein a tangent to the surface at thebeginning of said expansion chamber forms an angle in the range 20 to50, and wherein the walls of said funnel-shaped inlet port to saidthroat forms an angle in the range of 5 to 15 to the center line.

8. Process for drawing off a plurality of filaments withoutintermingling or twisting the filaments which comprises:

(a) aspirating a primary flow of gas to sound velocity in an aspiratingzone;

(b) smoothly expanding said aspirated primary gas to supersonic velocityin an expansion zone;

(c) thereafter passing said expanded primary gas into a draw-off zonehaving a uniform cross-section from end to end;

((1) conveying a plurality of filaments in a secondary flow of gasthrough said aspirating and expansion zones; and

(e) introducing said filaments and said secondary flow of gas centrallyinto said draw-off zone at a point where said expanded primary gasenters said drawolf zone or downstream therefrom, said expanded primarygas entering said draw-off zone in a direction parallel to the flow ofsaid filaments and applying drawing tension to said filaments withoutimpinging thereon.

9. Process of claim 8 wherein the expanded primary gas entering saiddraw-off zone brings said secondary gas to a supersonic velocity.

10. Process of claim 8 wherein the inlet pressure of said primary gas tosaid aspirating zone is between 10 and 50 atmospheres gauge.

11. Process of claim 8 wherein the inlet pressure of said primary gas tosaid aspirating zone is between 22 to 50 atmospheres gauge.

References Cited UNITED STATES PATENTS 2,971,243 2/ 1961 Burns 226972,971,267 2/ 1961 Berlyn 22697 2,971,683 2/1961 Paulsen 22697 3,559,8602/ 1971 East 22697 2,411,660 11/1946 Manning 154-101 2,437,263 3/ 1948Manning 188 2,622,961 12/ 1952 Finlayson et al. 28--1.4 3,341,394 9/1967Kinney 161-72 JAY H. WOO, Primary Examiner U.S. Cl. X.R.

